Millions of stranded airline passengers will be eligible for compensation payouts after the European court of justice (ECJ) ruled that they can claim for delays caused by technical problems.

In a case brought by the Dutch airline KLM, the judge decreed that unexpected technical problems can no longer count as an “extraordinary circumstance”, opening the door to claims of up to €600 (£437) a head.

Last year, the supreme court reached the same conclusion in a case brought by a passenger who wanted compensation for a 27-hour delay, but the decision was only legally binding in England and Wales.

However, the battle is far from over. Since the supreme court verdict, thousands of people who have tried to lodge a claim have been fobbed off by airlines. This week, Britain’s aviation regulator, the Civil Aviation Authority, began enforcement action against Ryanair to make the budget airline pay compensation to thousands of delayed passengers in the wake of the European court judgment.

Londoner Alan Macdonald was delayed eight hours when his Ryanair flight from Malta to London was grounded. Check-in staff and the captain blamed a technical fault, but when passengers tried to claim, Ryanair mysteriously changed its story. “Adverse weather conditions” were suddenly the cause and, since these counted as “extraordinary circumstances” beyond the airline’s control, it insisted compensation was not payable.

“It was only in a letter sent a month after my claim that weather was mentioned,” Macdonald says. “In their initial email to passengers, they declared the delay as being due to unspecified ‘exceptional circumstances’ and provided a link to an out-of-date list of such circumstances, including those that have been declared null in UK courts. This led other passengers to think they have no scope to claim.”

Macdonald contacted the Guardian, whereupon Ryanair said there had been a technical fault after all, and that he and his partner were due €400 each. The airline then blamed airport staff. “We rely on our handling agents for our information and, in this case, the cause was misreported and the customer was subsequently misinformed,” a spokesperson told us. “The report has since been rectified.”

So did the airline immediately contact all affected passengers to retract its misleading email? Of course not. “Those that I’ve kept in touch with haven’t received anything beyond the initial response of ‘no’,” Macdonald says. “Surely if one passenger is entitled to it there should be an automatic refund for all passengers?”

Ryanair insists this experience was an isolated case. But critics say airlines have been suffering collective amnesia about the cause of delays since the court ruling. “We often hear from passengers that they were told of ‘technical issues’ at the airport, only for it to change when the passenger goes to make a claim,” says a spokesperson from Bott & Co, a legal firm that specialises in flight delay claims and represented passengers’ interests in the KLM case. “In our experience most airlines do it in some cases.”

Since the court ruling, airlines have been turning “technical problems” into a “hidden manufacturing defect” which does count as an “extraordinary circumstance” and which would, if genuine, oblige the airline to ground its entire fleet.

“Before the ruling fewer than 5% of passenger claims represented by Bott & Co were met with the defence of hidden manufacturing defect,” says the spokesperson. “Now, around 79% of the claims we have going through the court system are using that defence. In some cases, airlines have even changed the defence from ‘technical problems’ to ‘hidden manufacturing defect’ on the very same claim. One major airline did not file a single ‘hidden manufacturing defect’ defence until March 2015, when we received 500 in the space of six weeks! We won on all those.”

Following this week’s ruling, enabling claims for technical faults, it is expected that the “hidden manufacturing defect” defence will become even more popular.

The reason airlines are so keen to reinvent the cause of a delay is because the levels of compensation stipulated by EC regulations can sometimes exceed the cost of the fare, and passengers have up to six years to lodge a claim. Most of those delayed more than three hours on a flight of up to 932 miles are entitled to €250, provided it departs or arrives at an EU airport. Long-haul travellers delayed more than four hours qualify for €600.

Paul Harvey who received compensation from Thomson for flight delays in Tenerife. Photograph: Graham Turner for the Guardian

Paul Harvey’s flight from Tenerife to Norwich was delayed by eight hours in January, and a form handed to the passengers blamed the crew’s legally required rest period after an inward-bound journey. When he requested statutory compensation, Thomson, the flight operator, replied (after 56 days) that “adverse weather conditions” had been the cause, and rejected his claim.

Harvey (above) contacted the Guardian and Thomson “reviewed” the case and decided that he and his companion were due €800 after all, although it declined to explain why it had changed its mind. The compensation equals the cost of Harvey’s entire trip. “I have donated £200 to Médecins Sans Frontières because I do find it odd that Thomson’s had to refund what was, in effect, the price of the holiday – or certainly more than the cost of the flight,” he says.

The statutory sums are supposed to deter airlines from allowing avoidable delays; in fact they seem to be deterring them from paying out. The British Air Transport Association attributes this reticence to badly drafted rules which the courts have had to clarify on a case-by-case basis, often disagreeing with each other in the process.

Ryanair argues that compensation “should reflect the airfare paid”. It says: “We have no issue paying compensation when it’s our responsibility, but the same rules should apply equally to competitive forms of transport, such as ferries, trains and buses.”

Following the CAA intervention the airline said it was unsure why enforcement action was being threatened when it was “complying fully” with EU 261 regulations.

Andrew Stevenson of Edinburgh was a Ryanair passenger whose claim for a four-hour delay from Carcassonne to Glasgow was affected. Speaking before this week’s ruling he said: “They are refusing to pay pending the distant possibility of a far-off ruling that will get them off the hook.” But the ECJ ruling, against which there is no appeal, should now result in a payout.

The CAA says it takes a dim view of airlines who flout the rules. “The law is clear, and airlines must pay passengers compensation if a flight was delayed by more than three hours as a result of a technical fault,” says a spokesperson.

The reality is that many passengers will still have to resort to the courts. Bott & Co is handling the cases of 1,500 claimants who have been fobbed off, and said that after the ECJ ruling it will now go back to court to enforce the claims.

A sky-high return from BA

A few minutes filling in an online form has netted us more than £1,700 – which may be because we flew with BA rather than Ryanair, writes Rupert Jones. In August 2014, my wife, our two kids and I flew from Heathrow to Los Angeles; our flight took off late because of a technical fault.

I didn’t give much thought to it, despite writing for a section of the Guardian that covers problems with flights and compensation. However, a high-profile court ruling last month involving Ryanair prompted my wife to look at whether we might be eligible for redress. She went on to the MoneySavingExpert website, checked how long our flight was delayed (via the FlightStats site), and made a claim using its free online “reclaim” tool.

Less than two weeks later, BA said we were entitled to €600 each – a total of £1,748.64. This week, it emailed again to say the money would be transferred into my wife’s account. “I’ve got nothing but praise for BA, who have dealt with it quickly and courteously,” she says.

Seeking redress

You can claim if an airline could reasonably have foreseen and prevented the cause of the delay. These include:

• Technical issues that should have been spotted during routine maintenance

• Airline strikes where due notice is given

• Knock-on effect of earlier strikes

• Poor timing of flight and turn-around times

• Inadequate official paperwork required before a flight can depart

You cannot claim if the delay is classed as an “extraordinary circumstance” – beyond an airline’s control – including:

• Air traffic control strike action

• Dangerous weather conditions

• Security alerts

• Manufacturing defects

• Unexpected damage to aircraft

There is a step-by-step guide on submitting a claim on the flight delays page of website MoneySavingExpert. There are also template letters to file a claim independently. Some airlines will pay up without a fuss, but others will ignore you. There is nothing to stop you bringing a small claims court claim yourself. Bott & Co will handle the claim, but it will take 27% of the reclaimed costs plus €25 per person.